Photocatalytic material, photocatalyst, photocatalytic product, lighting apparatus, and method of producing photocatalytic material

ABSTRACT

A photocatalytic material containing tungsten trioxide fine particles having an average particle diameter of 0.5 μm or smaller and a crystal structure of a monoclinic crystal system as a main component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2006-024918, filed Feb. 1, 2006;and No. 2006-152685, filed May 31, 2006, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a photocatalytic material excitable withvisible light, a photocatalyst using the photocatalytic material, aphotocatalytic product, a lighting apparatus and a method of producingthe photocatalytic material.

2. Description of the Related Art

As is conventionally known well, since a photocatalytic materialrepresented by titanium oxide is a material causing an effect such asstain prevention, deodorization, or the like, the photocatalyticmaterial has been used widely for a variety of applied products.However, since the main excitation light is ultraviolet ray, there is aproblem that no sufficient function can be obtained in the case ofapplications indoors where ultraviolet ray is slight. Conventionally, asa countermeasure to the problem, so-called visible light-responsivephotocatalysts have been enthusiastically investigated and developed.Specifically, those obtained by doping titanium oxide with nitrogen andthose obtained by depositing platinum on titanium oxide have beendeveloped. However, since the range of wavelength of visible light whichtitanium oxide photocatalyst excites is as narrow as 410 to 410 nm, thephotocatalytic function is insufficient under indoor illumination light.

Further, as photocatalysts other than the titanium oxide types, BiVO₄and perovskite type crystalline materials have been investigated.However, they have not yet become usable in terms of the properties andcost. Further, as other visible light-responsive photocatalysts,tungsten oxide and iron oxide have been investigated. Tungsten oxide hasa band gap energy of 2.5 eV and is colored with yellow, and therefore isadvantageous in the case of using it as a construction material.Tungsten oxide is a scarcely toxic and relatively economic material.

Further, tungsten oxide is relatively easily made available as anindustrial material. However, tungsten oxide is commercialized in theform of secondarily sintered large particles (1 to 100 μm). Therefore,the specific surface area is narrow and in the case of using tungstenoxide for a photocatalyst, the activity is low. Additionally, tungstenoxide has two crystal systems; a monoclinic system and a triclinicsystem, at a normal temperature. Accordingly, the photocatalyticactivity becomes unstable due to change of the crystal by a physicalimpact and it is difficult to produce a coating material using tungstenoxide. The photocatalytic effect of tungsten oxide by visible light isconfirmed by forming a film by reactive sputtering method (refer to Jpn.Pat. Appln. KOKAI Publication No. 2001-152130, or “Photocatalysts”, p676, issued on May 27, 2005, NTS Co.).

On the other hand, visible light-responsive photocatalysts usingtungsten powders have been investigated, but presently no sufficienteffect has been caused yet.

Tungsten oxide is stable in the form of tungsten trioxide (WO₃) innormal temperature atmosphere. However, tungsten trioxide has acharacteristic that the crystal structure is complicated and easilychangeable. In general, tungsten trioxide produced from ammoniumpara-tungstate and tungstic acid has a monoclinic crystal system.However, due to the stress at the time of treating a powder (forexample, crushing it in a mortar), the crystal structure is easilychanged to a triclinic crystal system (J. Solid State Chemistry 143, 2432(1999)). To improve the catalytic effect of the photocatalyst, it isneeded to prevent electrons excited by light and holes fromrecombination until they reach the surface. Accordingly, it is requiredto lessen defects to be the recombination centers as much as possible inthe crystal of the photocatalyst and to make the particle diameter assmall as possible.

So far, the tungsten oxide powder has not given a sufficientphotocatalytic effect. It is supposed that the reason for this isbecause crystal change partially occurs at the time of processing thepowder in pretreatment process and different crystals are intermixed,and the boundaries of the crystals become defects to cause recombinationof electrons and holes. In the case of the film formed by aconventionally known sputtering method, it is said that sufficientcatalytic effect can be obtained by using tungsten oxide of thetriclinic crystal system. However, no sufficient catalytic effect isobtained with tungsten oxide powder of the triclinic crystal system.

BRIEF SUMMARY OF THE INVENTION

An aim of the invention is to provide a photocatalytic material having ahigh catalytic effect and responsive to visible light by keeping aprescribed crystal structure, and a photocatalyst body and aphotocatalytic product using this material.

Another aim of the invention is to provide a lighting apparatuscomprising a visible light-responsive photocatalyst film which isexcellent in the photocatalytic effect, is scarcely colored withtungsten trioxide fine particles, and scarcely affects the lightingfunction.

Further, another aim of the invention is to provide a method ofproducing a tungsten trioxide photocatalytic material having stablecrystal structure and a high photocatalyst effect.

(1) A photocatalytic material of the present invention contains tungstentrioxide fine particles having an average particle diameter of 0.5 μm orsmaller and a crystal structure of a monoclinic crystal system as a maincomponent.

Herein, the average particle diameter of tungsten trioxide is preferablyin a range of 0.01 to 0.1 μm and most preferably in a range of 0.02 to0.05 μm. The inventors of the invention have made various investigationson the photocatalytic activity of tungsten trioxide. As a result, theyhave found that tungsten trioxide having the crystal structure ofmonoclinic crystal system and specified particle diameter is moreexcellent in the visible light response and photocatalytic activity thanthat having the crystal structure of triclinic crystal system, which hadbeen considered highly effective.

As the average particle diameter of the fine particles is smaller, thespecific surface area is larger and the ratio of electron-holerecombination tends to be decreased more. Therefore, it is convenientfor improving the photocatalytic activity. The lower limit of theaverage particle diameter possible to be formed stably is 0.01 μm. That“the tungsten trioxide fine particles with the monoclinic crystal systemare used as a main component” means that the triclinic crystal systemmay be mixed with the monoclinic crystal system. Particularly, if 50% bymass, preferably 70% by mass, of tungsten trioxide has the crystalstructure of monoclinic crystal system, an efficient photocatalyticeffect can be obtained. Further, the chemical formula of tungstentrioxide is WO₃. However, according to the analysis of the crystalstructure of the fine particles, even tungsten oxide having 2.8 or 2.9as an atomic ratio x of oxygen in WO_(x) may be defined as the tungstentrioxide of the invention as long as it has the crystal structure ofmonoclinic crystal system.

According to the above-mentioned photocatalytic material, it is madepossible to obtain a visible light-responsive photocatalytic materialexcellent in the photocatalytic effect by causing the photocatalyticactivity while keeping the crystal structure of the tungsten trioxidefine particles in the state of monoclinic crystal system.

(2) A photocatalyst body of the present invention comprises a layer ofthe photocatalytic material according to (1) formed on a substratesurface and a photocatalyst film containing tungsten trioxide fineparticles maintaining a crystal structure of a monoclinic crystal systemand formed on the layer of the photocatalytic material. According to theabove-mentioned photocatalyst body, it is made possible to obtain aphotocatalyst body having a photocatalyst film formed of thephotocatalytic material excellent in the photocatalytic effect.

(3) A photocatalytic product of the present invention comprises aphotocatalyst filter and a light emitting diode which radiates lightincluding at least blue color light to the photocatalyst filter, whereinthe photocatalytic material according to (1) is deposited on thephotocatalyst filter and tungsten trioxide fine particles maintain acrystal structure of a monoclinic crystal system after deposition.According to the photocatalytic product of the invention, it is madepossible to obtain a photocatalytic product comprising thephotocatalytic material excellent in the photocatalytic effect.

(4) A lighting apparatus of the present invention comprises a lightsource, a light transmissive cover substrate enveloping the lightsource, and a photocatalyst layer formed on an outer face or an innerface of the cover substrate and containing tungsten trioxide fineparticles having an average particle diameter of 0.1 μm or smaller and acrystal structure of a monoclinic crystal system.

In the lighting apparatus, it is made possible to obtain a photocatalystby using the photocatalyst layer containing tungsten trioxide fineparticles as a main component and adding 5 to 50% by weight, preferably10 to 20% by weight, of a binder component such as acryl-modifiedsilicon, silicone type resin, SiO₂, ZrO₂, and Al₂O₃ with high visiblelight and ultraviolet transmittance to the tungsten trioxide fineparticles. Use of the photocatalytic material mixed with such a bindercomponent makes it possible to form a photocatalyst layer at a roomtemperature by coating. Accordingly, there is no need to install specialfacilities such as a high temperature heating apparatus. On the otherhand, if the average particle diameter of the tungsten trioxide fineparticles exceeds 0.1 μm, the fine particles are seen to be colored withyellow, and therefore, the photocatalyst layer formed in the lightingapparatus or the radiation light is seen to be discolored. Accordingly,it is preferable to adjust the average particle diameter of the tungstentrioxide fine particles to be 0.1 μm or smaller. In addition, withrespect to the lighting apparatus, the photocatalyst layer may be formedusing the tungsten trioxide fine particles alone.

According to the lighting apparatus of the invention, the photocatalystlayer containing tungsten trioxide fine particles with an averageparticle diameter of 0.1 μm or smaller and having the monoclinic crystalsystem is formed on a substrate surface of a light transmissive cover ora reflection plate of the lighting apparatus. Therefore, it is madepossible to obtain the lighting apparatus provided with a visiblelight-responsive photocatalyst film excellent in the photocatalyticeffect, scarcely affecting the lighting effect and having hardlynoticeable coloration of the tungsten trioxide fine particles.

(5) A lighting apparatus of the present invention comprises a lightsource, a reflection plate substrate set optically on the opposite tothe light source, and a photocatalyst layer formed on the reflectionplate substrate and containing tungsten trioxide fine particles havingan average particle diameter of 0.1 μm or smaller and a crystalstructure of a monoclinic crystal system.

In the lighting apparatus, the photocatalyst layer contains the tungstentrioxide fine particles as a main component and may additionally containa prescribed amount of fine particles of titanium oxide,nitrogen-substituted titanium oxide or platinum-deposited titaniumoxide. The photocatalyst layer may be formed by adding 5 to 50% byweight, preferably 10 to 20% by weight, of a binder component such asacryl-modified silicon, silicone type resin, SiO₂, ZrO₂, and Al₂O₃ withhigh visible light and ultraviolet transmittance to the tungstentrioxide fine particles. The photocatalyst layer can be formed byheating the applied photocatalytic material at a temperature in a rangefrom a room temperature to 120° C.

(6) A method of producing a photocatalytic material of the presentinvention comprises the steps of producing a granular raw material byspraying an aqueous solution containing 1 to 20% by weight of ammoniumpara-tungstate in high temperature atmosphere, and forming tungstentrioxide fine particles having a crystal structure of a monocliniccrystal system by heating the granular raw material at 700 to 800° C.for 1 to 10 minutes. According to the method of producing thephotocatalytic material of the invention, since the granular rawmaterial is produced from fine liquid-phase colloid generated byspraying an aqueous solution, it is made possible to obtain crystallinephotocatalyst fine particles of tungsten trioxide with scarce crystalgrowth and few oxygen defects.

(7) A method of producing a photocatalytic material of the presentinvention comprises the steps of dissolving ammonium para-tungstate in awater-based solvent and successively carrying out recrystallization, andforming a tungsten trioxide photocatalytic material by firing theobtained crystal in conditions of 600° C. or higher for 15 seconds orlonger. Herein, as the ammonium para-tungstate, crystal obtained byprevious recrystallization of commercialized ammonium para-tungstate inwater may be used. Firing may be carried out in atmospheric air. Thefiring temperature and the firing time are determined based on the factthat the optimum conditions are 800° C. and 1 minute. However, an upperlimit of the firing temperature is 1000° C., and an upper limit of thefiring time is 15 minutes. The firing temperature exceeds 1000° C., aprimary grain size of WO₃ becomes large, activity is lessened. And, itis unfavorable that if the firing time exceeds 15 minutes,crystallization grows and its grains size increases.

According to the method of producing the photocatalytic material of theinvention, the visible light-responsive tungsten trioxide materialexcellent in photocatalytic activity can be obtained by firing therecrystallized ammonium para-tungstate at a prescribed temperature for aprescribed time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1A and 1B show schematic explanatory drawings of a fluorescentlamp according to the invention;

FIGS. 2A and 2B show conceptual explanatory drawings of a deodorizationunit according to the invention;

FIG. 3 shows X-ray diffraction data of monoclinic crystal system WO₃which is a main component of the photocatalyst powder of the invention;

FIG. 4 shows X-ray diffraction patterns of triclinic crystal system andmonoclinic crystal system of tungsten trioxide (WO₃);

FIG. 5 shows a characteristic drawing showing the comparison ofacetaldehyde decomposition effects in the case where the crystalstructures of tungsten trioxide differ;

FIG. 6 shows a conceptual drawing of a measurement apparatus employedfor obtaining the characteristic drawing of FIG. 5;

FIG. 7 shows a conceptual drawing of a production apparatus forproducing the photocatalytic material of the invention;

FIG. 8 shows a graph of particle size distribution (the relation amongfrequency, the particle diameter and the integrated penetration) afterdispersion;

FIG. 9 shows a graph of particle size distribution (the relation amongfrequency, the particle diameter and the integrated penetration) of theWO₃-dispersed coating material;

FIG. 10 shows a microscopic photograph of ammonium meta-tungstate as agranular raw material obtained in a third embodiment;

FIG. 11 shows a microscopic photograph of monoclinic crystal system typeWO₃ crystal photocatalyst fine particles obtained by rapid and shorttime heating of the granular raw material obtained in the thirdembodiment at 800° C. for 1 to 10 minutes;

FIG. 12 shows a characteristic drawing showing the acetaldehydedecomposition capability of the respective tungsten trioxidephotocatalyst fine particles obtained by firing at a temperature of 600°C., 700° C., 800° C., and 900° C. in a fourth embodiment;

FIG. 13 shows a characteristic drawing showing the acetaldehydedecomposition capability of the respective tungsten trioxidephotocatalyst fine particles obtained by firing at a temperature of 600°C., 700° C., 800° C., and 900° C. in the fourth embodiment;

FIG. 14 shows a characteristic drawing showing the acetaldehydedecomposition capability in the case where the firing time is changed tobe 30 seconds, 1 minute, 5 minutes, 10 minutes, and 15 minutes;

FIG. 15 shows a drawing showing the relation between the wavelength andthe reflectivity in the case of using WO₃ photocatalyst of a sixthembodiment and TiO₂ photocatalyst;

FIG. 16 shows a perspective view in the disassembled state of thelighting apparatus according to the sixth embodiment;

FIG. 17 shows an enlarged cross-sectional drawing of the main part ofFIG. 16; and

FIG. 18 shows the relation between the time and the acetaldehyderemaining ratio by using the lighting apparatus of a seventh embodimentin combination with a TiO₂ photocatalyst-bearing fluorescent lamp, theTiO₂ photocatalyst-bearing fluorescent lamp, and a TiO₂photocatalyst-bearing lighting apparatus in combination with the TiO₂photocatalyst-bearing fluorescent lamp.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the invention will be described more in detail withreference to drawings.

FIG. 1 is a cross-sectional view schematically showing the configurationof a fluorescent lamp according to the invention. FIG. 1A shows across-sectional view including the cut cross-sectional view and FIG. 1Bis a schematic cross-sectional view of a photocatalyst film, which isone component of the above-mentioned fluorescent lamp.

The reference numeral 10 in the drawing shows a fluorescent lamp as aphotocatalytic product and comprises a fluorescent lamp main body 20 anda photocatalyst film 30 formed on the surface of the fluorescent lampmain body 20. The fluorescent lamp main body 20 comprises a lighttransmissive electric discharge container 11, a phosphor layer 12, apair of electrodes 13 and 13, an electric discharge medium, which is notillustrated, and a base 14.

The container 11 is composed of a thin and long glass bulb 11 a and apair of flare stems 11 b. The glass bulb 11 a is made of soda-limeglass. Each flare stem 11 b is provided with a gas discharge pipe, aflare, an inner lead wire, and an outer lead wire. The gas dischargepipe is employed for discharging the gas out of the inside of thecontainer 11 by communicating the inside and outside of the container 11and enclosing an electric discharge medium. The gas discharge pipe issealed after the enclosure of the electric discharge medium. The flareis attached to both ends of the glass bulb 11 a to form the lighttransmissive electric discharge container 11. The base end of the innerlead wire is air-tightly buried in the inside of each flare stem 11 band the inner lead wire is connected with the outer lead wire. The tipend of the outer lead wire is buried in each flare stem 11 b and thebase end thereof is led outside of the light transmissive electricdischarge container 11.

The phosphor layer 12 contains three-light emitting type phosphors andformed in the inner face of the light transmissive electric dischargecontainer 11. The three-light emitting type phosphors are BaMgAl₁₆O₂₇:Eufor blue light emission, LaPO₄:Ce for green light emission, and Y₂O₃:Eufor red light emission. The pair of the electrodes 13 and 13 areconnected between the tip end parts of the pair of the inner lead wiresset on the opposite to each other at a distance in both inner ends ofthe light transmissive electric discharge container 11. Each electrode13 comprises a coil filament of tungsten and an electron emittingsubstance attached to the coil filament.

The electric discharge medium contains mercury and argon and is enclosedin the inside of the light transmissive electric discharge container 11.A proper amount of mercury is enclosed through the gas discharge pipe.Argon is enclosed at about 300 Pa in the light transmissive electricdischarge container 11. Each cap 14 comprises a cap main body 14 a and apair of base pins 14 b and 14 b. The cap main body 14 a has a cap-likeshape and attached to both end parts of the light transmissive electricdischarge container 11. The pair of the cap pins 14 b and 14 b aresupported in each cap main body 14 a while being insulated from eachother and respectively connected with the outer lead wire.

The photocatalyst film 30 is a film of a photocatalyst coating materialcontaining tungsten trioxide fine particles (average particle diameter:0.1 μm) as a main component and the film thickness thereof is about 0.5to 3 μm. The tungsten trioxide fine particles maintain the crystalstructure of the monoclinic crystal system even after completion of thecoating. The photocatalyst film 30 contains photocatalyst fine particles21 together with a binder 22 with excellent ultraviolet or visible lighttransmittance such as alumina fine particles, silica fine particles, orzirconia fine particles. The photocatalyst fine particles 21 arecomposed of tungsten trioxide fine particles 21 a and calcium carbonatefine particles 21 b attached to the surfaces of the tungsten trioxidefine particles 21 a. The binder 22 is added in an amount of 10 to 50% byweight to the tungsten trioxide fine particles 21 a. If acryl-modifiedsilicon and silicone type resins are used for the binder 22, thephotocatalyst film can be cured at 20 to 200° C. Further, the calciumcarbonate fine particles 21 b work as a substance for absorbing NO_(x)(nitrogen oxide) and SO_(x) (sulfur oxide). Accordingly, if there is noneed to suppress deterioration of the tungsten trioxide fine particles21 a due to NO_(x) and SO_(x), it is not essential to add the calciumcarbonate fine particles 21 b.

FIG. 2 is an explanatory drawing schematically showing the configurationof a deodorization unit according to the invention. FIG. 2A shows aschematic perspective view of the deodorization unit and FIG. 2B shows aschematic side face of the unit shown in FIG. 2A. FIG. 2B does not showtungsten trioxide fine particles for convenience.

The reference numeral 41 in the drawings shows a deodorization unit as aphotocatalytic product. A deodorization unit 41 comprises first andsecond, upper and lower, flat mesh-like filters 42 a and 42 b and athird filter 43 having corrugated cross-sectional shape and disposedbetween the filters 42 a and 42 b. Tungsten trioxide fine particles(average particle diameter: 0.1 μm) 44 of the invention are deposited onthe respective filters 42 a, 42 b, and 43. A plurality of GaNblue-emitting diodes 45 are installed under the second filter 42 b. Inthis case, in place of the diodes 45, white-emitting diodes usingphosphors excited by blue light may be installed. In the deodorizationunit with such a configuration, when air passes, for example, from theleft side to the right side through the third filter 43 between thefirst and the second filters 42 a and 42 b, the air is deodorized bybeing in contact with the tungsten trioxide fine particles deposited onthe respective filters 42 a, 42 b, and 43.

In the invention, the average particle diameter of tungsten trioxide(WO₃) fine particles is adjusted to be 0.5 μm or smaller and preferably0.1 μm or smaller. Herein, when the average particle diameter exceeds0.5 μm, the probability of occurrence of the reaction in the surfaces ofthe fine particles is decreased and no sufficient catalytic effect canbe obtained. Further, the crystal structure of the tungsten trioxide isthe monoclinic crystal system, and the crystal structure tends to easilychange to the triclinic crystal system only by crushing tungstentrioxide in a mortar. Accordingly, it is important to keep themonoclinic crystal system. FIG. 3 shows spectroanalysis spectrum of theblue-emitting diode 45 used in the deodorization unit shown in FIG. 2.It is understood from FIG. 3 that radiation light of the blue-emittingdiode 45 has a specific energy peak around 470 nm.

FIG. 4 shows an X-ray diffraction pattern graph of tungsten trioxide(WO₃) of the triclinic crystal system and monoclinic crystal system. TheX-ray diffraction pattern measurement is carried out as follows. Thatis, at first, using CuKα-beam (λ=0.15418 nm) as X-ray, a sample isrotated at an angle θ with respect to the incident X-ray beam.Simultaneously, the X-ray intensity (CPS) at every diffraction angle(2θ) is measured by a goniometer which rotates the detection partcomprising a proportional counter at 2θ. In FIG. 4, (a) shows the resultof triclinic crystal system WO₃ and (b) shows the result of monocliniccrystal system WO₃.

As is clear from FIG. 4, in comparison of the respective diffractionpatterns of triclinic crystal system and monoclinic crystal systemtungsten trioxide, most parts are analogous. However, it is confirmedthat the patterns considerably differ in the range of 30 to 35° of thediffraction angle 2θ. Particularly, there are a large peak unique to themonoclinic crystal system and a plurality of small peaks unique to thetriclinic crystal system at an angle 2θ=34.155°. This clearly shows thedifference between the two systems.

In the case of tungsten trioxide of the monoclinic crystal system, twopeaks exist in the 2θ range of 30 to 35° and in the case of tungstentrioxide of the triclinic crystal system, three or more peaks areconfirmed to exist in the same range. Further, ratios of the peak valueappearing in the 2θ range of 30 to 35° to the peak value in the 2θ rangeof 30 to 35° are as follows. That is, in the case of tungsten trioxideof the triclinic crystal system, the ratio is as low as 50 to 60%. Onthe other hand, in the case of tungsten trioxide of the monocliniccrystal system, the ratio is in a range from 70 to 95% and thedifference of the peak value is small.

FIG. 5 shows a characteristic drawing showing the comparison ofacetaldehyde decomposition effects in the case where the crystalstructures of tungsten trioxide differ. In FIG. 5, the curve a shows theresult using the WO₃ fine particles of the monoclinic crystal system ofthe invention (corresponding to (b) of the graph FIG. 4B); the curve bshows the result using WO₃ fine particles of the triclinic crystalsystem of Comparative Example (corresponding to (a) of the graph FIG.4A); and the curve c shows the result in the case of using nophotocatalyst and light radiation.

FIG. 6 shows a conceptual drawing of a measurement apparatus employedfor obtaining the characteristic drawing of FIG. 5. The referencenumeral 1 in the drawing shows a desiccator and a laboratory dish 2containing the photocatalyst is housed in the desiccator. A fan 3 isinstalled under the laboratory dish 2 in the desiccator 1. A multi-gasmonitor 5 is connected to an upper part and a side part of thedesiccator 1 through pipes 4. Further, a blue emitting LED light source6 for radiating light to the photocatalyst is attached slantingly to theupper part of the desiccator 1.

The design of the above-mentioned measurement apparatus is as follows.

Measurement box (desiccator) capacity: 3000 ccLight source: blue emitting LEDMeasurement device: multi-gas monitorIntroduced gas: equivalent to 10 ppm acetaldehyde

Blue emitting LED: 0.88 mW/cm² (UV-42) and 0.001 mW/cm² (UV-35)

Powder amount of tungsten trioxide fine particles: 0.1 g

It is made clear from FIG. 5 that the gas decomposition effect is higherin the curve a than in the curve b and thus the photocatalytic effect ofWO₃ of the monoclinic crystal system of the invention is moresignificant when visible light is radiated.

The photocatalyst coating material of the invention may include thosewhich contain the tungsten trioxide fine particles and keep themonoclinic crystal system of the tungsten trioxide fine particles aftercompletion of the coating. The photocatalyst coating material has asignificantly excellent function including the VOC removal by thephotocatalyst and suitable to be used for a deodorization filter to beused, for example, in an air purification apparatus.

The photocatalyst body of the invention may include those having astructure formed by applying the photocatalyst coating material to asubstrate surface and accordingly forming a photocatalyst film. Thephotocatalyst body may include tubular or bulb products such as afluorescent lamp; construction materials such as window glass, mirror,and tiles; sanitary products; filter parts of air conditioners anddeodorization apparatus; and optical appliances. However, applicationsand categories of the photocatalyst body are not particularly limited tothese exemplified spheres.

The photocatalyst product of the invention may include those comprisingthe above-mentioned photocatalyst coating material in combination withGaN blue-emitting diodes or incandescent light-emitting diodes usingphosphors excited by blue light, and those comprising the photocatalystfilter in combination with GaN blue-emitting diodes or incandescentlight-emitting diodes using phosphors excited by blue light. Herein, thephotocatalytic product practically includes a fluorescent lamp, alighting apparatus, and a deodorization unit.

In the invention, the photocatalyst fine particles are produced byemploying the production apparatus shown in FIG. 7. The productionapparatus comprises a spray dryer main body A, a gas-liquid mixing partB, a compressed air introduction part C, a solution introduction part D,and a powder recovery part E. The reference numeral 51 in the drawingshows a drying chamber equipped with a distributor 52 in the upper partthereof. Herein, the distributor 52 works as an air introduction inletfor heating the drying chamber 51 to 200° C. A spraying nozzle 53 and apipe 55 a equipped with a solenoid valve 54 are installed in the dryingchamber 51 while penetrating the distributor 52. The pipe 55 a works asan air introduction inlet for introducing air proper for pressurizingand atomizing an aqueous solution. A pipe 55 b is installed in the upperpart of the drying chamber 51 to suck air through. The pipe 55 b worksas a hot air suction port for heating the aqueous solution and air. Thepipe 55 a is branched to a pipe 55 c equipped with a needle valve 56.

The pipe 55 c is joined to the upper part of the spraying nozzle 53. Atube 59 for supplying a sample 57 to the spraying nozzle 53 by a pump 58is connected to the upper part of the spraying nozzle 53. The amount ofthe sample 57 to be supplied to the spraying nozzle 53 is made properlyadjustable by the pump 58. A cyclone 60 for taking out a product sprayedin an atomized state from the spraying nozzle 53 is connected to a sidepart of the drying chamber 51. A product container 61 for collecting thephotocatalyst fine particles and an aspirator 62 for gas discharge arerespectively connected to the cyclone 60.

A temperature sensor, which is not illustrated, is installed in theinlet side and outlet side of the drying chamber 51. Owing to thetemperature sensor, the temperature of air to be supplied to the dryingchamber 51 and the temperature of ambient air surrounding thephotocatalyst fine particles to be sent to the cyclone 60 are measured.The air to be supplied to the pipe 55 c is mixed with the sample 57supplied to the tube 59 in the upper side part of the spraying nozzle 53and sprayed in an atomized state from a lower part of the sprayingnozzle 53.

In the case of producing the photocatalyst fine particles using theproduction apparatus with the above-mentioned structure, the process maybe carried out as follows. At first, an aqueous solution containing 1 to20% by weight of ammonium para-tungstate (sample) is sent together withcompressed air to the spraying nozzle 53. Successively, the solution issprayed through the tip end of the spraying nozzle 53 in hot airatmosphere at 200° C. to obtain a granular raw material with a particlediameter of 1 to 10 μm. In this case, the compressed air is sent to theperiphery of the tip end of the spraying nozzle 53 from the pipe 55 a tosupply air to the granular raw material to be sprayed by the sprayingnozzle 53. Next, heating treatment is carried out at 700 to 800° C. for1 to 10 minutes in the drying chamber 51. Consequently, it is madepossible to produce photocatalyst fine particles containing tungstentrioxide fine particles as a main component and having an averageparticle diameter of 0.1 μm and the crystal structure of monocliniccrystal system. Successively, while the inner gas of the drying chamber51 is evacuated by an aspirator 62, the photocatalyst fine particles inthe drying chamber 51 are collected in the product container 61 by thecyclone 60.

Next, practical embodiments of the invention will be described.

First Embodiment

A photocatalyst powder according to the first embodiment was produced asfollows.

At first, ammonium para-tungstate (APT) was crushed by a bead mill or aplanetary mill and classified by centrifugation. Next, the obtained fineparticles were heated at 400 to 600° C. in atmospheric air to refine aphotocatalyst powder of tungsten trioxide fine particles having acrystal structure of the monoclinic crystal system.

In the first embodiment, the heating treatment at about 500° C. inatmospheric air gave tungsten trioxide fine particles having an averageparticle diameter of about 0.1 μm and the monoclinic crystal system. Theparticle size distribution data in this step is as shown in FIGS. 8 and9. Herein, FIG. 8 shows the particle size distribution (the relationamong the particle diameter, the frequency and the integratedpenetration) after dispersion. FIG. 9 shows the particle sizedistribution (the relation among the particle diameter, the frequencyand the integrated penetration) of the WO₃-dispersed coating material.From FIGS. 8 and 9, it is understood that the crystal is slightly grownand the particle size becomes larger by the heating treatment.

According to the photocatalyst powder of the first embodiment, since thepowder contains the tungsten trioxide fine particles with an averageparticle diameter of 0.1 μm as a main component and having a crystalstructure of the monoclinic crystal system, the visible light-responsivephotocatalyst powder with considerably improved photocatalytic functioncan be obtained.

Second Embodiment

A photocatalyst coating material for indoor according to a secondembodiment was produced as follows.

At first, tungsten trioxide fine particles and a trace amount of asurface treatment agent were mixed with an organic solvent (ethylalcohol) and dispersed for several hours by a bead mill. Successively,an inorganic binder (polysiloxane) in an amount of 30% by weight to thetungsten trioxide fine particles, an organic solvent (alcohol), and purewater in an amount of several % were added and again the dispersiontreatment was carried out to obtain the photocatalyst coating material.After that, calcium carbonate and magnesium hydroxide in amounts changedin a range of 0.1 to 10% by mole on the basis of the tungsten trioxidewere added to the obtained photocatalyst coating material and stirred toobtain samples. Next, the samples were applied to glass plates, acrylicplates, and fluorescent lamp glass tubes and then dried at 120 to 180°C. to produce coating samples.

They were put in BOX made of a stainless steel and having a capacity of1 m³ as an initial state. Successively, ultraviolet rays of 1 mW/cm²intensity were radiated to the glass plates and acrylic plates by a BLBlamp. The fluorescent lamps were lighted while being kept in the BOX asthey were to measure the effect of decomposing formaldehyde. After themeasurement, the samples were left in a room in the case of the glassplates and acrylic plates and the fluorescent lamps were subjected to alighting test in a common work office to measure the gas decompositioncapability for every week.

According to the second embodiment, magnesium oxide capable of easilyabsorbing SO_(x) and NO_(x) as compared with tungsten trioxide wasproperly added to the coating material containing the tungsten trioxidefine particles and the obtained photocatalyst coating material forindoor was used for forming a photocatalyst film on the fluorescent lampmain body. Consequently, effects such as disinfection and stainprevention unique to the photocatalyst film can be obtained. Further,deterioration of the photocatalyst film can be suppressed during the useand accordingly a fluorescent lamp with a long life can be obtained.

Third Embodiment

At first, an aqueous solution (sample) containing 4% by weight ofammonium para-tungstate was sent to the inside of a spraying nozzle 53shown in FIG. 7. Next, the solution was sprayed through the tip end ofthe spraying nozzle 53 in hot air-blowing atmosphere at 200° C. toatomize particles with a particle diameter of 1 to 10 μm and obtained agranular raw material. In this case, compressed air was sent to theperiphery of the tip end of the spraying nozzle 53 from a pipe 55 a tosupply oxygen to the photocatalyst fine particles sprayed by thespraying nozzle 53. If the concentration of the aqueous solution is 4%by weight, a granular raw material of ammonium para-tungstate with 40 to400 nm can be obtained. Next, rapid and short time heating underconditions of 800° C. for 1 to 10 minutes was carried out in the dryingchamber 51 to forcibly dry the above-mentioned raw material andre-crystallized the material. As a result, tungsten trioxidephotocatalyst fine particles containing tungsten trioxide fine particlesas a main component, having an average particle diameter of 0.5 μm orsmaller, preferably 0.1 μm or smaller, and a crystal structure of themonoclinic crystal system were obtained. Successively, while the insideair of the drying chamber 51 was evacuated by an aspirator 62, thephotocatalyst fine particles in the drying chamber 51 were collected ina product container 61 by a cyclone 60.

According to the third embodiment, compressed air is sent to theperiphery of the tip end of the spraying nozzle 53 through the pipe 55 aand oxygen is supplied to the photocatalyst fine particles, so that theWO₃ crystal photocatalyst fine particles with few oxygen defects can beobtained. Further, the rapid and short time heating under conditions of800° C. for 1 to 10 minutes is carried out in the drying chamber 51, sothat the WO₃ crystal photocatalyst fine particles with scarce crystalgrowth can be obtained.

FIG. 10 shows a microscopic photograph of ammonium meta-tungstate as agranular raw material obtained in the third embodiment. FIG. 11 shows amicroscopic photograph of monoclinic crystal system type WO₃ crystalphotocatalyst fine particles obtained by rapid and short time heating ofthe granular raw material obtained in the third embodiment at 800° C.for 1 to 10 minutes. From FIG. 10, it is understood that although thereis a slight difference, the granular raw material of ammoniummeta-tungstate with an even particle diameter can be obtained.

Fourth Embodiment

The fine particles of this embodiment are tungsten trioxide fineparticles produced by heating and firing a raw material, which isobtained by dissolving commercialized ammonium para-tungstate in awater-based solvent and then carrying out recrystallization, at a hightemperature for 1 minute in atmospheric air.

FIG. 12 shows a characteristic drawing showing the acetaldehydedecomposition capability of the respective tungsten trioxidephotocatalyst fine particles obtained by changing the firing temperatureto 600° C., 700° C., 800° C., and 900° C. in the fourth embodiment. InFIG. 12, the curve (a) shows the result in the case of 600° C.; thecurve (b) shows the result in the case of 700° C.; and the curve (c)shows the result in the case of 800° C.

FIG. 13 shows a characteristic drawing showing the acetaldehydedecomposition capability of the respective tungsten trioxidephotocatalyst fine particles obtained by firing at a temperature of 800°C., 900° C., and 1000° C. In FIG. 13, the curve (a) shows the result inthe case of 800° C.; the curve (b) shows the result in the case of 900°C.; and the curve (c) shows the result in the case of 1000° C.

The decomposition capability evaluation shown in FIGS. 12 and 13 wascarried out in the following conditions. At first, 0.1 g of tungstentrioxide fine particles were put in a laboratory dish and set in aclosed container with a capacity of 200 cc. Next, a blue emitting LEDwas installed in the container in a manner that the light having theelectroluminescence spectrum shown in FIG. 3 can be radiated to thephotocatalyst fine particles. Successively, acetaldehyde gas wasintroduced in a proper concentration to adjust the acetaldehydeconcentration in the container to be 10 ppm and simultaneously the blueemitting LED was lighted and the gas concentration fluctuation wasmeasured with the lapse of time. The concentration measurement wascarried out based on the output of a gas sensor installed in thecontainer and evaluation was carried out by relative comparison of theoutput values.

The graphs of FIGS. 12 and 13 show the relative values (%) showing theoutput of the sensor corresponding to the concentration of acetaldehydein the axis of ordinates. The container is filled with the gas within 20to 30 seconds after introduction. After that, it is seen that theconcentration is gradually decreased by the decomposition effect of thephotocatalyst. In this connection, in FIGS. 12 and 13, the maximum valueof the sensor output is set to be 100% for convenience.

From FIGS. 12 and 13, it is understood that the decomposition effect ishighest in the case where the crystal, which is obtained by dissolvingthe commercialized ammonium para-tungstate as a raw material in waterand carrying out recrystallization for fine granulation, is fired at800° C. Therefore, the firing temperature is found to be preferable in arange from 700 to 900° C. In such a manner, the photocatalytic materialof the fourth embodiment is more excellent in the visible light-responseand has higher photocatalytic activity than tungsten oxide obtainedsimply by firing a commercialized product.

Fifth Embodiment

Fine particles of this embodiment are tungsten trioxide fine particlesobtained by the following procedure. That is, at first commercializedammonium para-tungstate was dissolved in a water-based solvent. Next,the particles obtained by recrystallization were fired at 800° C. for aprescribed time in atmospheric air to produce the fine particles.

FIG. 14 shows a characteristic drawing showing the acetaldehydedecomposition capability in the case where the firing time was changedto be 30 seconds (the curve (a)), 1 minute (the curve (b)), 5 minutes(the curve (c)), 10 minutes (the curve (d)), and 15 minutes (the curve(e)). The decomposition capability evaluation conditions and theillustrated contents of the graph of FIG. 14 are the same as those ofFIG. 12.

From FIG. 14, it is understood that high gas decomposition capabilitycan be obtained if the firing temperature is adjusted to be 1 to 5minutes.

Sixth Embodiment

A lighting apparatus according to a sixth embodiment of the inventionhas the configuration shown in FIGS. 16 and 17. Herein, FIG. 16 shows aperspective view of the lighting apparatus in the disassembled state andFIG. 17 shows an enlarged cross-sectional drawing of the main part ofFIG. 16. The sixth embodiment relates to the lighting apparatus using atransmissive shade (cover) in which a ultraviolet cut layer mainlycontaining a ultraviolet shutting material is formed in the inner face.

A lighting apparatus 71 is provided with a disk-like apparatus main body72. The apparatus main body 72 is directly attached to the ceiling partby a hooking sealing installed in the ceiling and an adaptor to beattached to the hooking sealing. A step part 73 with a large thicknesssize is installed in the center part of the apparatus main body 72. Acircular aperture part 74 in which the adaptor is inserted formechanical connection is formed in the center part of the step part 73.

Further, two lamp sockets 75 and two lamp holders 76 are formed in thecircumferential part of the apparatus main body 72. Two circular lightemitting tubes of fluorescent lamps 77 to be light sources (for example,light emitting tubes of fluorescent lamps with 32 W and 40 W andmutually different outer diameters) are electrically and mechanicallyconnected to the lamp sockets 75. Further, the two light emitting tubes77 are mechanically supported by the lamp holders 76 and installedconcentrically around the step part 73. A socket 78 is formed in aportion of the aperture part 74. A lamp 79 such as a baby bulb isinstalled in the socket 78.

A shade 80 as an optical part for lighting is attached to the apparatusmain body 72 so as to be detached from the apparatus main body 72 andcover the apparatus main body 72 and the under and side parts of membersattached to the apparatus main body 72. The shade 80 is provided with acover substrate 81 for lighting made of an acrylic material. The coversubstrate 81 is light transmissive just like glass or resins and formedto have a curved and smoothly downward projected shape. A photocatalystlayer 82 containing the tungsten trioxide fine particles having acrystal structure of the monoclinic crystal system and an averageparticle diameter of 0.1 μm is formed in the outer face of the substrate81.

The above-mentioned photocatalyst layer 82 was formed as follows. Thatis, at first, commercialized ammonium para-tungstate (APT) with a sizeof about 100 μm as a raw material was crushed by a bead mill or aplanetary mill to have an average particle diameter of 0.05 to 0.1 μm,and the obtained fine particles were heated at 500° C. for 8 hours inatmospheric air. Accordingly, tungsten trioxide fine particles wereproduced. Next, the tungsten trioxide fine particles and a bindercomponent were dispersed in and mixed with a solvent to obtain a coatingmaterial. Successively, the coating material was applied to thesubstrate 81 by a spray gun and dried to form the layer.

According to the sixth embodiment, since the photocatalyst layer 82 wasformed on the surface of the substrate 81 using the coating materialobtained by dispersing the tungsten trioxide fine particles and thebinder component, there is no need to carry out heating treatment at ahigh temperature after the coating formation. As a result, the substratesuch as an organic substrate as an object to be coated is provided withthe photocatalyst function, and even in the case where the coating isformed on the acrylic cover outer face, sufficient activity can beobtained.

In the sixth embodiment, although the photocatalyst layer 82 is formedon the outer face of the substrate 81, the configuration is not limitedthereto and the layer may be formed integrally by mixing thephotocatalytic material with the resin composing the substrate 81.

FIG. 15 shows the relation between the wavelength and the reflectivityin the case of using WO₃ photocatalyst (curve (a)) of the sixthembodiment and TiO₂ photocatalyst (curve (b)). The curve (c) of FIG. 15shows the acrylic cover transmittance and the curve (d) shows thespectroscopic distribution of light radiated from a three-light emittingtype fluorescent lamp. From FIG. 15, it is understood that tungstentrioxide of the sixth embodiment efficiently absorbs, as the energy forphotocatalyst activation, blue- and green-visible light with wavelengthof 400 to 500 nm transmitted through the acrylic cover.

Seventh Embodiment

This embodiment provides a configuration of a reflection substrate madeof a color steel plate for lighting and coated with a WO₃ photocatalystlayer. The photocatalyst layer was formed as follows.

That is, commercialized ammonium para-tungstate (APT) with a size ofabout 100 μm as a raw material was crushed by a bead mill or a planetarymill to have an average particle diameter of 0.05 to 0.1 μm. Next, theobtained fine particles were heated at 500° C. for 8 hours inatmospheric air to produce tungsten trioxide fine particles.Successively, the tungsten trioxide fine particles and a bindercomponent were dispersed in and mixed with a solvent to obtain a coatingmaterial. Further, the coating material was applied to the reflectionsubstrate made of the color steel plate by a spray gun and dried to formthe layer.

The effect similar to that of the sixth embodiment can be obtained inthe seventh embodiment.

FIG. 18 shows the relation between the time and the acetaldehyderemaining ratio in the case of using the lighting apparatus of theseventh embodiment in combination with a TiO₂ photocatalyst-bearingfluorescent lamp (curve (a)), the TiO₂ photocatalyst-bearing fluorescentlamp (curve (b)), and a TiO₂ photocatalyst-bearing lighting apparatus incombination with the TiO₂ photocatalyst-bearing fluorescent lamp (curve(c)). As is clear from the graph of FIG. 18, the photocatalyst layerformed on the surface of the reflection plate substrate of the lightingapparatus is more excellent in the photocatalyst effect in the case ofusing monoclinic crystal system tungsten trioxide fine particles than inthe case of using TiO₂ fine particles as before.

1. A photocatalytic material containing tungsten trioxide fine particleshaving an average particle diameter of 0.5 μm or smaller and a crystalstructure of a monoclinic crystal system as a main component.
 2. Aphotocatalyst body comprising a layer of the photocatalytic materialaccording to claim 1 formed on a substrate surface and a photocatalystfilm containing tungsten trioxide fine particles maintaining a crystalstructure of a monoclinic crystal system and formed on the layer of thephotocatalytic material.
 3. A photocatalytic product comprising aphotocatalyst filter and a light emitting diode which radiates lightincluding at least blue color light to the photocatalyst filter, whereinthe photocatalytic material according to claim 1 is deposited on thephotocatalyst filter and tungsten trioxide fine particles maintain acrystal structure of a monoclinic crystal system after deposition.
 4. Alighting apparatus comprising a light source, a light transmissive coversubstrate enveloping the light source, and a photocatalyst layer formedon an outer face or an inner face of the cover substrate and containingtungsten trioxide fine particles having an average particle diameter of0.1 μm or smaller and a crystal structure of a monoclinic crystalsystem.
 5. A lighting apparatus comprising a light source, a reflectionplate substrate set optically on the opposite to the light source, and aphotocatalyst layer formed on the reflection plate substrate andcontaining tungsten trioxide fine particles having an average particlediameter of 0.1 μm or smaller and a crystal structure of a monocliniccrystal system.
 6. A method of producing a photocatalytic materialcomprising the steps of producing a granular raw material by spraying anaqueous solution containing 1 to 20% by weight of ammoniumpara-tungstate in high temperature atmosphere, and forming tungstentrioxide fine particles having a crystal structure of a monocliniccrystal system by heating the granular raw material at 700 to 800° C.for 1 to 10 minutes.
 7. A method of producing a photocatalytic materialcomprising the steps of dissolving ammonium para-tungstate in awater-based solvent and successively carrying out recrystallization, andforming a tungsten trioxide photocatalytic material by firing theobtained crystal in conditions of 600° C. or higher for 15 seconds orlonger.